Merge pull request #1186 from ymiftah/bugfix/check_empty_not_nothing

bugfix: Table Data Parser can have undefined inputs

src/parsers/power_system_table_data.jl

@@ -275,7 +275,7 @@ function System(
     )
 
     for (val, parser) in parsers
-        if !isnothing(val)
+        if !isempty(val)
             parser(sys, data)
         end
     end